fix: load designs off-thread and cache recent thumbnails as PNGs

apps/solvecraft-cli/src/main.rs

@@ -3,7 +3,7 @@
 //! ```text
 //! solvecraft-cli run <script.json|design.solvecraft|part.step|mesh.3mf> [--in design|part.step|mesh.3mf] [--out FILE]... [--save FILE] [--quiet]
 //! solvecraft-cli eval <script.json|design.solvecraft|part.step> (alias: inspect) measurements as JSON
-//! solvecraft-cli bench-open <design.solvecraft> [--parse-only] loading timings as JSON lines
+//! solvecraft-cli bench-open <design.solvecraft | part.step> [--parse-only] loading timings as JSON lines
 //! solvecraft-cli snapshot <script|design> --out shot.png [--width W] [--height H] [--view iso|front|top|…]
 //! solvecraft-cli exec <command> [json-params]                 run one command on an empty design
 //! solvecraft-cli commands                                     the command registry as JSON
@@ -32,7 +32,7 @@ const USAGE: &str = "usage:
   solvecraft-cli run <script.json|design.solvecraft|part.step> [--in design.solvecraft|part.step] [--out FILE]... [--save FILE] [--quiet] [--results]
   solvecraft-cli run --in <design.solvecraft|part.step> [--out FILE]...
   solvecraft-cli eval <script.json|design.solvecraft|part.step>     (alias: inspect; or --in FILE)
-  solvecraft-cli bench-open <design.solvecraft> [--parse-only]
+  solvecraft-cli bench-open <design.solvecraft | part.step> [--parse-only]
   solvecraft-cli snapshot <script|design> --out shot.png [--width W] [--height H] [--view iso|front|back|top|bottom|left|right]
   solvecraft-cli exec <command> [json-params]
   solvecraft-cli commands
@@ -357,17 +357,26 @@ fn cmd_bench_edit(args: &[String]) -> Result<(), String> {
 
 /// Separate file reading, JSON decoding/repair, timeline evaluation and display meshing.
 fn cmd_bench_open(args: &[String]) -> Result<(), String> {
-    let path = args.first().ok_or("usage: solvecraft-cli bench-open <design.solvecraft> [--parse-only]")?;
+    let path = args.first().ok_or("usage: solvecraft-cli bench-open <design.solvecraft | part.step> [--parse-only]")?;
     let t = std::time::Instant::now();
     let len = std::fs::metadata(path).map_err(|e| format!("{path}: {e}"))?.len();
-    if len > solvecraft_engine::io::MAX_DESIGN_BYTES as u64 {
+    let step = solvecraft_engine::io::is_step_path(path);
+    let limit = if step { solvecraft_engine::io::MAX_STEP_BYTES } else { solvecraft_engine::io::MAX_DESIGN_BYTES };
+    if len > limit as u64 {
         return Err(format!("{path}: file too large"));
     }
     let bytes = std::fs::read(path).map_err(|e| format!("{path}: {e}"))?;
     let read_ms = t.elapsed().as_secs_f64() * 1000.0;
     println!("{}", json!({"step": "read", "ms": read_ms, "bytes": bytes.len()}));
     let t = std::time::Instant::now();
-    let doc = solvecraft_engine::io::read_design(&bytes).map_err(|e| e.to_string())?;
+    let doc = if step {
+        let imported = solvecraft_engine::io::step_import_feature(&bytes, path).map_err(|e| e.to_string())?;
+        let mut doc = solvecraft_engine::doc::Document::new(&imported.name);
+        doc.add_feature(imported.kind, Some(&imported.name)).map_err(|e| e.to_string())?;
+        doc
+    } else {
+        solvecraft_engine::io::read_design(&bytes).map_err(|e| e.to_string())?
+    };
     let parse_ms = t.elapsed().as_secs_f64() * 1000.0;
     println!("{}", json!({"step": "parse", "ms": parse_ms, "features": doc.features.len()}));
     if args.iter().any(|a| a == "--parse-only") {